1. Field of the Invention
The invention relates to a fuel supply control device and control method for an engine of which an injector is connected to an intake pipe via a fuel passage.
2. Description of Related Art
A bifuel (dual-fuel) engine that may be used by switching between gaseous fuel and liquid fuel is practically used as a vehicle-mounted engine. In an engine of this type, it may be difficult to directly install both an injector for liquid fuel injection and an injector for gaseous fuel injection in an intake pipe in terms of installation space. In such a case, for example, as described in Japanese Patent Application Publication No. 2010-242559 (JP 2010-242559 A), there is a configuration that a gaseous fuel injector is installed at a position remote from an intake pipe and gaseous fuel injected from the gaseous fuel injector is introduced into the intake pipe via a fuel passage formed of a pipe, a hose, or the like.
Note that, in the engine of this type, gaseous fuel sometimes remains in the intake pipe immediately after switching from gaseous fuel supply to liquid fuel supply. Then, a fuel supply control device for an engine, described in Japanese Patent Application Publication No. 2001-193511 (JP 2001-193511 A), immediately after switching from gaseous fuel supply to liquid fuel supply, corrects the injection amount of liquid fuel so as to reduce on the basis of the remaining amount of gaseous fuel in the intake pipe.
Incidentally, in the thus configured engine in which the gaseous fuel injector is connected to the intake pipe via the fuel passage, at the time of initial fuel injection after switching from liquid fuel to gaseous fuel, fuel injection is carried out in a state where the fuel passage is not filled with gaseous fuel.
In a state where the fuel passage is filled with fuel, as fuel is injected from the gaseous fuel injector, fuel in the injected amount is pushed out from the fuel passage and is supplied into the intake pipe. Thus, at this time, gaseous fuel in the same amount as the injected amount is supplied into intake air. On the other hand, in a state where the fuel passage is not filled with gaseous fuel, even when fuel is injected from the gaseous fuel injector, gaseous fuel is not supplied into intake air until the fuel passage is filled with gaseous fuel. Therefore, as shown in FIG. 7, if a fuel injection command is issued for initial fuel injection after switching fuel as in the case of the subsequent fuel injection, not all the injected fuel is supplied into intake air, and the amount of supplied fuel does not reach a required amount at the initial injection, so the air-fuel ratio temporarily deviates toward a lean side immediately after switching fuel. Then, as a result, the combustion condition deteriorates to thereby lead to deterioration of drivability and emissions.
Note that such inconvenience can similarly occur even in the case where injected fuel is liquid but in an engine in which an injector is connected to an intake pipe via a fuel passage having a volume larger than a certain extent.